The present invention relates to a self-adjusting brake, particularly a drum-type brake equipped with internal brake shoes which are self-adjusting to compensate for wear of the brake lining.
More particularly, the present invention relates to a self-adjusting brake having a brake drum, two brake shoes, a brake cylinder and a stationary brake shoe support for floatingly mounting the brake shoes. The latter are arranged interiorly of the brake drum and coact with it, the ends of the brake shoes being curved and pressed against the brake cylinder and the brake shoe support by means of return springs which also serve to lift the brake shoes off the brake drum when the brake is in non-actuated condition. One of the two brake shoes is the primary brake shoe and the other is the secondary brake shoe, these designations being taken with respect to the direction of rotation of a wheel with which the brake is associated. The primary brake shoe is the one the leading edge of which, during normal rotation of the drum, contacts the brake cylinder, whereas the secondary brake shoe contacts the brake cylinder with its trailing edge. Each brake shoe has a T-shaped cross section constituted by a flange forming the top of the T and a web which forms the stem of the T, the flange of each brake shoe carrying a brake lining, with each web having associated with it means which form an inclined surface coacting with a respective stationary pin, the inclination of the inclined surfaces being such that the amount of the play between the brake lining carried by the brake shoes and the brake drum, when the brake is in non-actuated condition, remains substantially constant during displacement of the brake shoes resulting from wear of the brake lining.
Various efforts have been made to develop self-adjusting brakes of the above type while reducing the very high costs incident to such brakes, such as interlocks, detents, wedges and friction members. In one such self-adjusting brake, as shown, for example, in German Patent Application No. 1,077,077 published March 3rd, 1960, the inclined surfaces are arranged approximately in the middle of the brake shoe, at the outer edge of the web, and are constituted by the material of which the web itself is made. The precise inclination of these surfaces required for trouble-free operation must of necessity be determined experimentally. This, however, is not wholly satisfactory because frequently a long series of tests must be carried out until a practical result is obtained. The brake arrangement has a total of four return springs, there being two for each brake shoe. Both of the return springs associated with each brake shoe are inclined with respect to the longitudinal axis of the associated brake cylinder, one of them being connected at its two ends to the ends of the two brake shoes which abut the brake cylinder in question whereas the other of the two springs has one connected to the brake cylinder and the other end to the respective brake shoe. The configuration and effective lines of action of the springs must be such that when the brake is in its non-actuated condition, all of the forces exerted by the springs are brought into a stable equilibrium so as to avoid any forces or moments which would tend to move the brake shoes out of the concentric position. It is not readily apparent how this is or can be done, or what the direction of the effective forces is.
It is, therefore, the primary object of the present invention to provide a self-adjusting brake which overcomes the above drawbacks, namely, a brake which incorporates a self-adjusting device and which can be built in such a way as to obtain the desired result.